1. Field of the Invention
This invention relates to a vacuum calibrator tool for sizing molten plastic extrudate as it leaves an extruder and enters a vacuum tank containing water through which the extrudate passes as it cools and hardens. The vacuum calibrator tool has a film of water created between the extrudate and the tool to lubricate the extrudate and to permit the tool to accurately size and shape the extrudate as it enters the vacuum sizing tank.
2. Description of the Prior Art
Efforts have been made in the plastics industry to provide for the controlled cooling and accurate sizing of molten plastic extrudate after it leaves the plastic extruder. The extrudate can easily be deformed if excessive pressure is applied to the outer surface of the extrudate. To prevent this type of deformation, vacuum cooling and sizing tanks have been developed that have a water bath within a vacuum chamber which prevents excessive pressure from being applied to the surface of the extrudate as it cools. An example of such an arrangement is found in U.S. Pat. No. 5,340,295 entitled "Vacuum Sizing Apparatus With Controlled Vacuum".
When very small diameter tubing or other small extrudate is cooled in a vacuum chamber, it is essential to initially accurate size and shape the extrudate as it enters the vacuum chamber. Because the extrudate is somewhat fragile at that point, various tools employing water rings have been utilized to produce a film of water around the extrudate as it enters a sizing tool and proceeds through the sizing tool into the vacuum chamber.
It has been found that the prior vacuum calibrator tools that have been used for sizing the extrudate as it enters the vacuum chamber have not adequately provided for sufficient water film to lubricate the interior of the tool and to permit the extrudate to move readily through the tool without coming into contact with the surfaces of the tool. The present invention provides a vacuum calibrator tool that has an extended area of water lubrication of the extrudate after it enters the sizing tool so that the extrudate may be accurately sized and shaped. This sizing tool is particularly useful for sizing extrudate of small diameter medical tubing, electronic shrink tubing, and fiber optic cable where close tolerances are required for the finished product.